/* 拖拽的区域样式 */
.holder {
    min-height: 200px;
    background: #eee;
    margin: 2em;
    padding: 1em;
    border: 0px dotted #eee;
    border-radius: 10px;
    transition: .3s all ease-in-out;
}

/* 拖拽时用jQuery为其添加边框样式的class */
.holder-ondrag {
    border: 8px dotted lightskyblue;
}